On the first day of his visit to Medley, Princess Casamassima's country house, Hyacinth Robinson and his hostess take a walk together in the park. Before the walk begins, the princess goes off to change, leaving Hyacinth in the library:

She left him for a short time, giving him the last number of the Revue des Deux Mondes to entertain himself withal, and calling his attention, in particular, to a story of M. Octave Feuillet (she should be so curious to know what he thought of it); and reappeared... presenting herself to our young man, at that moment, as a sudden incarnation of the heroine of M. Feuillet's novel, in which he had instantly become emersed.

Feuillet, once a famous French novelist and playwright, is now largely forgotten. This is perhaps why the allusion to him in The Princess Casamassima has received very little attention from the commentators on James's novel. It is surprising, though, because this reference to Feuillet is a very significant clue to understanding much in The Princess Casamassima, especially Hyacinth's and the princess's friendship, the princess's supposedly capricious personality, and the end of the novel.